For many years "Black Boxes" were synonymous with airplane crashes. The acquired (downloaded) data from these boxes were an invaluable tool for accident investigative engineers.
In the early 70's, the National Transportation Safety Board (NTSB) made several recommendations that the automobile manufacturers (OEM) and National Highway Traffic Safety Administration (NHTSA) gather data on crashes using onboard sensing and recorders. As a direct result certain air bag equipped vehicles had recorders incorporated within.
Electronic sensors are gaining wide use in today's vehicles, which are primarily driven by the automobile industry's move towards electronically controlled systems. Through various methods (algorithms), these systems gather information (data) about the vehicle. Onboard computers (Electronic Control Module / OBD I / II) allowed the technician to check the operation of the engines and other vital components.
As the design of supplement restrain system (SRS - air bags), anti-lock brakes (ABS) and stability control systems, additional sensors and processors were needed. These new ECM's were capable of storing data, which includes resultants of fault errors. Henceforth, the "Black Box" was born.
All vehicles that are equipped with airbag(s) have three (3) basic components. They are as follows:
The Bag is construct of a woven material similar to nylon, which is folded like a parachute. They are coated with talc like powder that lubricates the air bag material for storage.
The Inflation System is similar to a solid rocket booster. This solid material ignites which burns extremely hot and rapidly to create gas. This action inflates the nitrogen gas (pulsed) via a chemical reaction of sodium azide (NaN3) and potassium nitrate (KNO3).
The Sensor is an electrical and/or mechanical device, which triggers a firing squib that activates the inflation systems and deploys the airbag(s).
The on-board computer's (ECM / OBD I / II) data is stored in two types of categories. They are as follows:
Non-Deployment Incident is an event that is severe enough to gather information from the sensors but NOT severe enough to deploy the air bag(s).
Deployment Incident is an event that is severe enough to gather information from the sensors and to deploy the air bag(s).
In both types of incidents the vehicle's processor (RAM) stores in memory, pre and post crash data.
The "Black Box" can record informational data, such as: engine / vehicle speed (5 seconds before impact), brake status (5 seconds before impact), throttle position(s), and even the state of the driver's seat belt switch (on/off). The combination of this information along with other engineering factors will indeed revolutionize the field of motor vehicle accident investigation.
For information on the legal ramifications of black boxes, please see this associated article.